1. Field of the Invention
The present invention relates to a charge control apparatus and a method for controlling the same.
2. Description of the Related Art
Conventionally, as a known technology, an auxiliary power supply (such as a secondary power supply or secondary battery) is provided to make a backup of data stored in a volatile memory such as a dynamic random access memory (DRAM) installed in an electronic device in preparation for power-down of the device.
The auxiliary power supply is charged by a main power supply of the electronic device to accumulate electric charges before the main power supply is powered down. Then, the accumulated electric charges are discharged when the device is powered down. Since the auxiliary power supply has only a limited charge capacity, it may be overcharged if the charging is continued beyond its limit (i.e., in a fully charged state). This may cause an adverse effect on lifetime of the auxiliary power supply.
An example of technologies for avoiding such an overcharge is discussed in Japanese Patent Application Laid-Open No. 9-56078. In this document, a fully-charged condition is detected by measuring a voltage of the auxiliary power supply, and an operation mode is switched to a trickle charge mode to reduce a current value for charging the auxiliary power supply.
Recently, a power-saving mode is widely employed, in which the power supplied to part of the device is cut off when no operation state lasts for a predetermined time period to save energy consumption in the device.
However, in the power-saving mode, the power supplied to a control unit (such as a central processing unit (CPU)) may be cut off. The control unit is configured to detect the fully-charged condition by measuring a voltage of the auxiliary power supply or detect whether a predetermined time period has lapsed after the charging starts. More specifically, the control unit may fail to detect the fully-charged condition or the time lapsed after the start of the charging, so that the auxiliary power supply may be continuously charged even when it is fully charged. As a consequence, the power supply becomes overcharged.